The Filling Ratio Effect on the Overshoot Phenomenon of Vertical Straight Wickless-Heat Pipe with Low Temperature Source Mukhsinun Hadi Kusuma1,a), Mulya Juarsa1,b), Nandy Putra2,c), Anhar Riza Antariksawan3,d), Muhammad Subekti1,e), Surip Widodo1,f)

Abstract. Vertical straight wickless-heat pipe (VSWHP) is now being chosen as one of the most efficient and
inexpensive passive cooling system technology. One potential application of VSWHP is to remove the heat generation in
a water cooling tank under accident condition in small modular reactor. The objective of this investigation is to know the
influence of filling ratio on the overshoot phenomenon of VSWHP with low temperature source. A series of experimental
investigation on vertical straight wickless-heat pipe was carried out with variation of working fluid filling ratio charged
in to VSWHP of 60, 80, and 100%, with constant value of temperature source of 60°C and coolant volumetric flow rate
of 8 L/min. The experiment results obtained show that, with lower temperature source, filling ratio of 60% resulted faster
overshoot phenomenon inside the vertical straight wickless-heat pipe. The ideal amount of filling ratio charged in the
heat pipe depends on the temperature source in the evaporator section. For low temperature source, the lower filling ratio
will accelerate the occurrence of the overshoot phenomenon and natural circulation in the VSWHP.
Keywords: Filling ratio; Heat pipe; Overshoot, Natural circulation, Passive cooling system